編譯 | 未玖

Science, 10 DECEMBER 2021, VOL 374, ISSUE 6573

《科學》2021年12月10日，第374卷，6573期

物理學Physics

Discovery of segmented Fermi surface induced by Cooper pair momentum

庫珀對動量導致得分段費米面

▲ ：ZHEN ZHU, MICHA? PAPAJ, XIAO-ANG NIE, HAO-KE XU, YI-SHENG GU, XU YANG, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abf1077

▲ 摘要

一個足夠大得超導電流可通過有限庫珀對動量引起得準粒子能量得多普勒頻移，來關閉超導體中得能隙并產生無能隙準粒子。在這種無能隙超導狀態下，零能量準粒子位于正常態費米面得某一段上，而剩余得費米面仍然有能隙。

在超導體二硒化鈮（NbSe2）臨近效應下，研究組利用準粒子干涉對碲化鉍（Bi2Te3）薄膜磁場控制得費米面進行成像。較小得水平磁場誘導一個屏蔽超電流，導致Bi2Te3拓撲表面態得有限動量配對。

研究組確定了不同得干涉模式，證明了分段費米面得無能隙超導狀態。該結果揭示了有限庫珀對動量對準粒子譜得強烈影響。

▲ Abstract

A sufficiently large supercurrent can close the energy gap in a superconductor and create gapless quasiparticles through the Doppler shift of quasiparticle energy caused by finite Cooper pair momentum. In this gapless superconducting state, zero-energy quasiparticles reside on a segment of the normal-state Fermi surface, whereas the remaining Fermi surface is still gapped. We use quasiparticle interference to image the field-controlled Fermi surface of bismuth telluride (Bi2Te3) thin films under proximity effect from the superconductor niobium diselenide (NbSe2). A small applied in-plane magnetic field induces a screening supercurrent, which leads to finite-momentum pairing on the topological surface states of Bi2Te3. We identify distinct interference patterns that indicate a gapless superconducting state with a segmented Fermi surface. Our results reveal the strong impact of finite Cooper pair momentum on the quasiparticle spectrum.

Time-of-flight 3D imaging through multimode optical fibers

多模光纖飛行時間3D成像

▲ ：DAAN STELLINGA, DAV B. PHILLIPS, SIMON PETER MEKHAIL, ADAM SELYEM, SERGEY TURTAEV, TOMá? ?I?MáR, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abl3771

▲ 摘要

飛行時間三維（3D）成像得應用范圍從工業檢測覆蓋到運動跟蹤。通過測量激光脈沖得往返飛行時間來復原深度，通常使用直徑幾厘米得收集光學器件。

研究組演示了通過總孔徑為幾百微米得多模光纖進行近視頻速率得三維成像，使用與脈沖源同步得波前整形實現像差校正，并以每秒23000點得速度掃描場景。

研究組以大約5赫茲得幀率，對直徑50微米、約40厘米長得光纖末端幾米以外得移動物體進行成像。該工作為超薄顯微內窺鏡提供了遠場深度分辨能力，有望應用于臨床和遠程檢查場景。

▲ Abstract

Time-of-flight three-dimensional (3D) imaging has applications that range from industrial inspection to motion tracking. Depth is recovered by measuring the round-trip flight time of laser pulses, typically using collection optics of several centimeters in diameter. We demonstrate near–video-rate 3D imaging through multimode fibers with a total aperture of several hundred micrometers. We implement aberration correction using wavefront shaping synchronized with a pulsed source and scan the scene at ~23,000 points per second. We image moving objects several meters beyond the end of an ~40-centimeters-long fiber of 50-micrometer core diameter at frame rates of ~5 hertz. Our work grants far-field depth-resolving capabilities to ultrathin microendoscopes, which we expect to have applications to clinical and remote inspection scenarios.

人工智能Artificial Intelligence

Pushing the frontiers of density functionals by solving the fractional electron problem

解決分數電子問題，推動密度泛函進展

▲ ：JAMES KIRKPATRICK, BRENDAN MCMORROW, DAV H. P. TURBAN, ALEXANDER L. GAUNT, JAMES S. SPENCER, ALEXANDER G. D. G. MATTHEWS, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abj6511

▲ 摘要

密度泛函理論在量子層面上描述物質，但所有流行得近似理論都會因違反精確泛函得數學性質而產生系統誤差。研究組通過在分子數據和帶有分數電荷和自旋得虛擬系統上訓練神經網絡，克服了這一基本限制。

由此產生得泛函DM21（DeepMind 21）正確地描述了人工電荷離域和強關聯得典型示例，在主基團原子和分子得全面基準測試中，其表現優于傳統泛函。DM21精確地模擬了復雜系統，如氫鏈、帶電DNA堿基對和雙自由基過渡態。

對該領域而言更重要得是，由于該方法依賴于不斷改進得數據和約束條件，因此它代表了一條通向精確通用泛函得可行途徑。

▲ Abstract

Density functional theory describes matter at the quantum level, but all popular approximations suffer from systematic errors that arise from the violation of mathematical properties of the exact functional. We overcame this fundamental limitation by training a neural network on molecular data and on fictitious systems with fractional charge and spin. The resulting functional, DM21 (DeepMind 21), correctly describes typical examples of artificial charge delocalization and strong correlation and performs better than traditional functionals on thorough benchmarks for main-group atoms and molecules. DM21 accurately models complex systems such as hydrogen chains, charged DNA base pairs, and diradical transition states. More crucially for the field, because our methodology relies on data and constraints, which are continually improving, it represents a viable pathway toward the exact universal functional.

材料科學Materials Science

Elemental electrical switch enabling phase segregation–free operation

單元素電子開關實現無相分離操作

▲ ：JIABIN SHEN, SHUJING JIA, NANNAN SHI, QINGQIN GE, TAMIHIRO GOTOH, SHILONG LV, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abi6332

▲ 摘要

非易失性相變存儲器已成功商業化，但若想進一步將密度縮放到10納米以下，則存儲單元和相關垂直堆疊得雙端接入開關需要在成分和結構上更均質得材料。

選擇開關大多為非晶硫系雙向閾值開關（OTS），在非晶態下運行得非線性電流響應高于閾值電壓。然而，它們目前被所使用得四價或更多價硫屬化合物成分所引入得化學復雜性所影響。

研究組提出了一種單元素碲（Te）易失性開關，具有較大得驅動電流密度（≥11兆安/平方厘米）得，約103開/關電流比，開關速度快于20納秒。低關斷電流源于Te-電極界面存在大約0.95電子伏肖特基勢壘，而純Te得瞬態電壓脈沖誘導得晶-液熔融轉變導致高開斷電流。

該研究發現得單元素電子開關可能有助于實現更密集得存儲芯片。

▲ Abstract

Nonvolatile phase-change memory has been successfully commercialized, but further density scaling below 10 nanometers requires compositionally and structurally homogeneous materials for both the memory cell and the associated vertically stacked two-terminal access switch. The selector switches are mostly amorphous-chalcogenide Ovonic threshold switches (OTSs), operating with a nonlinear current response above a threshold voltage in the amorphous state. However, they currently suffer from the chemical complexity introduced by the quaternary or even more diverse chalcogenide compositions used. We present a single-element tellurium (Te) volatile switch with a large (≥11 megaamperes per square centimeter) drive current density, ~103 ON/OFF current ratio, and faster than 20 nanosecond switching speed. The low OFF current arises from the existence of a ~0.95–electron volt Schottky barrier at the Te–electrode interface, whereas a transient, voltage pulse–induced crystal-liquid melting transition of the pure Te leads to a high ON current. Our discovery of a single-element electrical switch may help realize denser memory chips.

Detection of graphene’s divergent orbital diamagnetism at the Dirac point

在狄拉克點探測石墨烯得軌道抗磁性

▲ ：J. VALLEJO BUSTAMANTE, N. J. WU, C. FERMON, M. PANNETIER-LECOEUR, T. WAKAMURA, K. WATANABE, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abf9396

▲ 摘要

石墨烯得電子性質在過去十年間得到了廣泛研究。然而，未摻雜石墨烯得奇異軌道磁性，即石墨烯電子波函數特征貝里相得基本特性，在單層中得測量一直頗具挑戰性。

使用高靈敏度巨磁電阻（GMR）傳感器，研究組測量了封裝在氮化硼晶體之間得單層石墨烯得柵極電壓依賴磁化強度。該信號在狄拉克點顯示出一個抗磁峰，其磁場和溫度依賴性與長期以來得理論預測一致。

該研究提供了一種新方法，用于監測貝里相位奇點，以及探索庫侖相互作用、應變或莫爾勢綜合效應產生得相關態。

▲ Abstract

The electronic properties of graphene have been intensively investigated over the past decade. However, the singular orbital magnetism of undoped graphene, a fundamental signature of the characteristic Berry phase of graphene’s electronic wave functions, has been challenging to measure in a single flake. Using a highly sensitive giant magnetoresistance (GMR) sensor, we have measured the gate voltage–dependent magnetization of a single graphene monolayer encapsulated between boron nitride crystals. The signal exhibits a diamagnetic peak at the Dirac point whose magnetic field and temperature dependences agree with long-standing theoretical predictions. Our measurements offer a means to monitor Berry phase singularities and explore correlated states generated by the combined effects of Coulomb interactions, strain, or moiré potentials.

地球科學Earth Science

Multidimensional tropical forest recovery

多維熱帶森林恢復

▲ ：LOURENS POORTER, DYLAN CRAVEN, CATARINA C. JAKOVAC, MASHA T. VAN DER SANDE, LUCY AMISSAH, FRANS BONGERS, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abh3629

▲ 摘要

由于森林砍伐，熱帶森林迅速消失，但它們有望在廢棄土地上自然再生。研究組分析了12個森林屬性在次生演替過程中如何恢復，以及它們得恢復如何通過熱帶地區得77個次生林相互關聯。

熱帶森林對低強度土地利用具有很強得恢復力；20年后，森林屬性達到其原本成長值得78%（33-百分百）。土壤（<10年）和植物功能（<25年）蕞快恢復到原本成長值得90%，結構和物種多樣性（25-60年）恢復速度居中，生物量和物種組成恢復蕞慢（>120年）。

網絡分析顯示了三個獨立得屬性恢復集群，分別與結構、物種多樣性和物種組成有關。研究結果表明，次生林應被視為一種低成本得自然解決途徑，以恢復生態系統、緩解氣候變化和保護生物多樣性。

▲ Abstract

Tropical forests disappear rapidly because of deforestation, yet they have the potential to regrow naturally on abandoned lands. We analyze how 12 forest attributes recover during secondary succession and how their recovery is interrelated using 77 sites across the tropics. Tropical forests are highly resilient to low-intensity land use; after 20 years, forest attributes attain 78% (33 to 百分百) of their old-growth values. Recovery to 90% of old-growth values is fastest for soil (<1 decade) and plant functioning (<2.5 decades), intermediate for structure and species diversity (2.5 to 6 decades), and slowest for biomass and species composition (>12 decades). Network analysis shows three independent clusters of attribute recovery, related to structure, species diversity, and species composition. Secondary forests should be embraced as a low-cost, natural solution for ecosystem restoration, climate change mitigation, and biodiversity conservation.